Generally a semiconductor element generates more heat as output power goes up. To maintain the performance of the semiconductor element, a heat dissipation plate used for a semiconductor packages has various kinds of structures.
For example, Japanese laid-open patent application No. 2001-144237 discloses a graphite sheet lamination heat conductor combined with thin metal plates and graphite sheets, which is excellent in thermal conductivity as compared with a metal material. And a graphite sheet lamination heat conductor is proposed to radiate heat from an electronic device.
The above-mentioned graphite sheet lamination heat conductor can perform with high heat conduction characteristics. However, in case it is used in the semiconductor package with a ceramic substrate, a bonding part with the ceramic substrate may be damaged by a heat deformation, since the thermal expansion coefficient of the graphite sheet lamination heat conductor differs from greatly that of the ceramic substrate.
On the other hand, Japanese patent No. 3862737 discloses a material for a heat dissipation plate that brings the thermal expansion coefficient of the material close to that of a ceramic substrate, which constitutes a semiconductor element, by laminating copper layers and molybdenum layers alternately.
However, the heat-conduction efficiency of the above-mentioned material is not satisfactory. When an output power of the semiconductor element goes up and a heating value rises further, it becomes difficult to cope with the increase in heating value without increasing a heat dissipation area.